The present invention relates to a method and apparatus for measuring the rate of flow of a liquid through a conduit. It particularly relates to a method and apparatus for measuring the rate of flow of hydrocarbons in production wells. Most particularly, it relates to a method and apparatus for measuring the rate and flow in production oil or water injection wells, and most especially relates to measurement of rates of flow in production oil wells where more than one source of flow opens into a common well head.
When extracting a flow of production fluids such as oil, from a well, it is important to be able to measure the rate of flow from the well head, and the contribution to the flow which comes from different sources opening into the common well head. In horizontal wells for hydrocarbon production, it is important for optimal recovery to know from which part of the reservoir the flow emanates. In multilateral wells, it is desirable to know how much each lateral contributes to the total production of the reservoir. If a particular lateral is producing too low a flow, it is then possible to take remedial action to increase its contribution.
Well bores are lined with casings whose approximate cross-sectional area is known. The free internal cross-sectional area of production tubing is also known. It is possible to derive a measure of the volume of flow at a specific location by measuring the linear flow-rate, or velocity, at that location.
It is known to measure flow-rates using measuring devices such as propellor driven flow meters. These are difficult to install within a well. The well has very limited cross sectional area thus limiting the size of device that may be installed. Propeller driven flow-rate meters are particularly difficult to install in horizontal wells or sub-sea wells. They are also difficult to install when a number of devices are required at different locations. The present invention seeks to provide a method and apparatus apt for the measurement of flow rate in horizontal wells, vertical wells, sub-sea wells and into the various parts of multilateral wells. The present invention also seeks to provide a method and apparatus for measuring flow rate at a plurality of points, unrestrained by the limitations imposed by the small cross-section of a well bore.
As well as the use of propeller driven devices such as spinner flow-meters, which turn at a rate dependent on the velocity of well fluids flowing past and are lowered down the well on an electric cable or wireline, apt for high flow-rate wells, it is also known in low flow-rate wells, which produce typically less than 1,000 barrels of oil a day, to use a radioactive tracer ejector tool. A radioactive marker (or tracer) is ejected into the oil flow. Gamma ray detectors are mounted above the ejection port on the tool. The ejector has to be replenished with tracers. The amount of time required for the marker or tracer to pass the gamma ray detectors gives a measure of the flow rate in the well. Gamma ray sources are a health hazard and require close custody and a monitoring. The present invention seeks to provide a method and apparatus for measuring flow rate in wells which has the same utility as the use of radioactive sources but lacks the health hazard associated with the radioactive tracer and which can remain permanently installed.
The prior art systems, in horizontal wells, both require deployment using coiled tubing. This is a very expensive proposition, and in sub-sea wells neither a wireline nor coiled tubing deployment systems can be used due to the limited access from the surface. The present invention seeks to provide a method and apparatus that can be so deployed without the expense of coiled tubing.
The present invention seeks to provide a non-invasive method and apparatus that can be pre-installed with the well, or subsequently at further work on the well, that is capable of monitoring fluid flow rate in well bores along reservoir intervals.
According to a first aspect, the present invention consists in an apparatus for measuring fluid flow in a conduit, said apparatus comprising: a temperature sensor for measuring and providing indication of the temperature of the fluid at at least first and second temperature measuring points spaced by a known distance along the conduit; a heat exchanger selectably operable to alter the temperature of the fluid upstream from said temperature measuring points; and a timer, responsive to said output of said temperature sensor to measure the time difference of arrival of the temperature altered fluid at said first and second temperature measuring points.
According to a second aspect, the present invention consists in a method for measuring fluid flow in a conduit, said method comprising the steps of: measuring the temperature of the fluid at a minimum of two temperature measuring points spaced by a known distance along the conduit; altering the temperature of the fluid upstream from said temperature measuring points; and measuring the time difference of arrival of the temperature altered fluid at said first and second temperature measuring points.
The first aspect of the invention further provides that the heat exchanger is operable to alter the temperature of the fluid for a selectable time.
The first aspect of the invention further provides an apparatus including a flow arrester, selectably operable to arrest the flow of the fluid in the conduit, the flow arrester being operable to arrest the flow of the fluid while the heat exchanger alters the temperature of the fluid, and the flow arrester valve being operable to allow the fluid to flow while the heat exchanger does not alter the temperature of the fluid.
The first aspect of the invention further provides that the temperature sensor can be a fibre optic cable, disposed along the conduit and operative to monitor temperature at a plurality of known, spaced locations along the length of the fibre optical cable.
The first aspect of the invention further provides that the heat exchanger can be operative to heat the fluid or, alternatively, to cool the fluid.
The first aspect of the invention further provides that the heat exchanger can be a gas expansion cooler, can comprise a throttle for cooling the gas and a cooling coil for the throttled gas to extract heat from the fluid, and can comprise a pressure relief valve, operative to allow gas to pass to be expanded if the gas supply pressure exceeds a predetermined limit.
The first aspect of the invention further provides that the apparatus can be for use where the fluid can be a hydrocarbon or water, where the hydrocarbon can be oil and where the conduit can be a hydrocarbon or water well.
The first aspect of the invention further provides that the flow arrester can be a selectably operable surface valve.
The first aspect of the invention further provides an apparatus which can be for use where the conduit has a plurality of flow sources, the apparatus comprising: a plurality of heat exchangers, each heat exchanger being downstream from a respective flow source; the temperature sensor being operative to measure and indicate the temperature at respective first and second points downstream from each heat exchanger; and the timer being operative to measure the time difference of arrival of temperature altered fluid at each respective pair of the first and second temperature measuring points.
The first aspect of the invention further provides an apparatus for use where the cross-sectional area of the conduit is known, the apparatus comprising computation means to calculate the volume rate of flow past the heat exchanger or heat exchangers, where the computation means can also calculate the volume rate of flow from each flow source.
The second aspect of the invention further provides a method including the step of altering the temperature of the fluid for a selectable time.
The second aspect of the invention further provides a method including the further step of arresting the flow of the fluid while altering the temperature of the fluid, and thereafter allowing the fluid to flow while not altering the temperature of the fluid.
The second aspect of the invention further provides a method including the use of a fibre optic cable, disposed along the conduit and operative to monitor temperature at a plurality of known, spaced locations along the length of the fibre optical cable.
The second aspect of the invention further provides a method wherein the step of altering the temperature of the fluid can involve heating the fluid or can involve cooling the fluid.
The second aspect of the invention further provides that the step of cooling the fluid includes the step of gas expansion and can include throttling the gas and passing the throttled gas through a cooling coil for the throttled gas to extract heat from the fluid; and can also include the use of a pressure relief valve to allow gas to pass to be expanded only if the gas supply pressure exceeds a predetermined limit.
The second aspect of the invention further provides a method for use where the fluid can be a hydrocarbon or water, where the hydrocarbon can be oil, and where the conduit can be a hydrocarbon or water well.
The second aspect of the invention further provides a method where the step of arresting the flow of the fluid can include the use of a selectably operable surface valve.
The second aspect of the invention further provides a method, for use where the conduit has a plurality of flow sources, the method comprising the steps of: altering the temperature of the fluid at a plurality of points, each downstream from a respective flow source; measuring the temperature at respective first and second points downstream from each point whereat the temperature has been altered; and measuring the time difference of arrival of temperature altered fluid at each respective pair of the first and second temperature measuring points.
The second aspect of the invention further provides a method for use where the cross-sectional area of the conduit is known, including the step of computing the volume rate of flow past the point or points whereat the temperature of the fluid has been altered.
The second aspect of the invention further provides a method including the step of calculating the volume rate of flow from each flow source.